HP 8903B repair

I really like my HP8903B audio analyzer. While PC based systems can outperform it in some areas, I like the robustness and simplicity of this standalone device. However it failed with “Error 14”. The analyzer is almost 20 years old, this can happen.

The modular design makes debugging relatively easy. After removing the analog front-end card, the analyzer worked again. Ok, there is a problem with this card. Looking at the card there was no obvious problem. Further debugging showed the one rail of the analog power supply was out-of-spec 13V instead of 15V. Looking at this on the oscilloscope showed a huge amount of ripple. At this point it was obvious that at least a capacitor in the power supply had a problem. There are 3 huge capacitors in the power supply, 2 for the analog +/-15V and another one for the digital 12V and 5V. Checking these capacitors showed that one of them was defective. Have a look at these huge parts. I replaced them with more modern caps (the black ones in the picture):

The replacement was done in a few minutes, as these are screw-in capacitors. There is no need to solder anything.

Looking at the picture now I think, I should also clean the device ;-)

Was this the root cause of “Error 14”? Let’s power it on again:

Yes, it is working again – great. If you ever get this error with your HP8903, check the power supply first.